The present invention relates to a method of producing WC/Co cemented carbide by chemically adding a grain growth inhibitor of WC/Co cemented carbide, and more particularly, to the method of producing WC/Co cemented carbide by adding a grain growth inhibitor during the initial production step of W and Co powders, which are the main components of said cemented carbide.
Generally, as for WC/Co cemented carbides, compression molding is carried out while adding cobalt powder, which is a binding agent, to the extremely hard intermetallic compound (e.g., tungsten carbide). Then, it is heated at a high temperature, followed by sintering. These cemented carbides are used as materials for cutting tools, such as bits or dills.
The mechanical properties of said WC/Co cemented carbides are affected by the amount of binding metals (i.e., cobalt), and the grain size of WC. Moreover, the mechanical characteristics thereof are affected by the distances between the WC grains. In general, as the WC grains are reduced into finer particles, the mechanical characteristics thereof are enhanced. Hence, for inhibiting grain growth, WC/Co cemented carbide is produced with addition of a grain growth inhibitor.
As for the conventional method of producing WC/Co cemented carbides, for resolving the problems arising from the abnormal growth of WC grains, a grain growth inhibitor, such as VC, TaC, or carbide, is added to the WC/Co cemented carbide powder by a mechanical methods (i.e., ball-milling). However, there are difficulties and limitations with respect to homogeneously mixing the cemented carbide powder of fine grain particles into the grain growth inhibitors of 1.0 xcexcm in size. Consequently, even after such mixing, the distribution of grain growth inhibitors is non-homogeneous, which in turn leads to the problem of partial abnormal growth of WC grains after the sintering process.
Accordingly, in solving the aforementioned problems, the technical objective of the present invention lies in providing a method of producing WC/Co cemented carbide by chemically adding a grain growth inhibitor for enhancing the degree of reduction into fine grain particles and the homogeneity thereof. In this regard, the production process is simplified by simultaneous reduction and carburization of cemented carbide powder and grain growth inhibitors by homogeneously mixing the same at a molecular level. In particular, in order to achieve such homogeneity, a growth grain inhibitor (i.e., VC, TaC, or Cr based water-soluble salt) in solution is added therein during the initial step of powder production.
In order to achieve the aforementioned technical objective, WC/Co cemented carbide is produced by:
preparing a precursor powder by spray-drying an initial solution of a mixture of water-soluble salts of W and Co, which are the main components of said cemented carbide;
adding and mixing a water-soluble salt including a grain growth inhibitor during mixing of said water-soluble salts of W and C;
desalting the precursor powder to remove salts by heating said precursor powder so as to obtain desalted oxide composites powder;
ball-milling to mix said desalted oxide powder and carbon black, resulting in composite oxides of fine particles; and
preparing a composite cemented powder, by carburization and reduction, by heating said composite oxides of fine particles in a non-oxidative atmosphere.
Therefore, with respect to the conventional production process of precursor powder of cemented carbides, the present invention comprises mixing water-soluble salts of V, Ta, or Cr component (i.e., grain growth inhibitor) to the water-soluble salts of W and Co, which are the main components of cemented carbides.
The present invention is explained in detail as follows: The present invention comprises mixing by dissolving water-soluble metal salt for grain growth inhibitors, for example, ammonium meta-vanadate (AMV), Ta-chloride, or Cr-nitrate, to the aqueous solution containing water-soluble salt of W, for example, ammonium metatungstate ((NH4)6(H2W12O40).4H2O,AMT) and water-soluble salt of Co, for example, Co-nitrate(Co(NO3)2.6H2O), which are the main components of cemented carbide.
Of course, the cemented carbide powder is produced by first preparing the precursor powder by spray-drying, followed by desalting the precursor powder, and then ball-milling said precursor powder and carbon black for mixing and pulverizing the power for carburization, followed by actual carburization and reduction.